The latter chipset is the Rambus chipset for the processor, and for the purposes of the review, VR-Zone has compared Intel's own D845HV motherboard for the desktop with Abit's TH7II-RAID board.
This is a pretty detailed look at the specifications of the i845 and the 850. It's quite interesting that Abit, who we met with earlier this week, believes like quite a few other mobo companies, that Rambus is still, very much, a viable option for the Pentium 4.
The conclusion, as you'd expect, is that the 850, using RIMMs outperforms the SDRAM based i845, but the piece says that there are some apps where the latter chipset performs "reasonably well".
Price is the real reason why people will choose the i845, the reviewer suggests, with La Intella positioning these boards as ripe for the mass market.
Of course the situation is complicated by other P4 chipsets that are, or will be available soon, such as the Via P4X266, the SiS and the ALi chipsets.
You can find the review here. µ